The case of a Singaporean caught spying for China in the US has reawakened fears over China recruiting intelligence assets on an island state which has won trust among Western governments while keeping on good terms with Beijing.

Jun Wei Yeo, a 39-year-old academic who also goes by the name Dickson Yeo, pleaded guilty in a US court on Friday to acting as an illegal agent of Chinese intelligence. He will be sentenced in October and faces up to 10 years in prison....